But the indictment and Medicaid suspensions didn't deter Medicare from continuing to allow the doctors to treat elderly and disabled patients — and didn't stop the physicians from billing taxpayers for their services.

In 2012, Medicare paid Greenbain more than $862,000, according to newly released data on Medicare payments to physicians. Tran received $155,000.

Greenbain and Tran were among dozens of doctors identified by ProPublica who kept getting Medicare payments after they were suspended or terminated from state Medicaid programs, indicted or charged with fraud, or had settled civil allegations of submitting false claims to Medicare.

Outlays to these doctors amounted to more than $6 million in 2012, ProPublica's analysis shows. That's only a small fraction of the $77 billion Medicare has publicly reported paying that year for doctors' visits and outpatient services in its Part B program. But it signifies a hole in regulators' ability to protect the program — and patients-- against fraud and abuse, say current and former government officials and fraud experts.

The total dollars paid to sanctioned doctors is likely much higher. Only a handful of states post online the names of doctors terminated from Medicaid programs in a way that can be accurately matched to Medicare Part B payments.

"If you've been suspended or terminated in one of the federal programs ... I would think that you'd be suspended in the other programs, just as a basis of good practice," said Louis Saccoccio, chief executive of the National Health Care Anti-Fraud Association.

Part B payments to doctors were released last week for the first time. A court injunction that had kept the information secret for 35 years was lifted last year as a result of a lawsuit by Dow Jones & Co., parent company of the Wall Street Journal.

Aaron Albright, a spokesman for the Centers for Medicare and Medicaid Services, said he could not discuss the status of individual doctors, such as Greenbain and Tran, both of whom were finally barred from billing Medicare this month.

Albright said the Medicare payment data may not reflect money already recovered by his agency or held back from providers suspended from billing the program.

Preventing improper payments is a top priority for CMS, Albright said. The agency has employed new enrollment screening techniques to prevent high-risk providers from getting into the system, he said, and is using advanced data analytics to spot fraudulent billing before payments are made.

Last year, ProPublica reported that doctors who had been booted from Medicaid — or who had been disciplined by state medical boards — were able to continue prescribing medications to beneficiaries in Medicare's drug program. The finding prompted Sen. Charles Grassley (R-Iowa) to push for better coordination.

Among the physicians ProPublica found who continued to collect Medicare Part B payments after being flagged by law enforcement or other oversight agencies:

Dr. Lawrence Eppelbaum, a Roswell, Ga., pain doctor convicted last year of inducing patients to be treated at his Atlanta pain clinic by paying their travel fees through a purported charity he controlled. Eppelbaum was indicted on the charges in March 2011, but Medicare paid him $500,000 to treat 80 patients the following year. This February, Eppelbaum was sentenced to 50 months in prison and fined $3.5 million. He is appealing. In a sentencing memorandum, Eppelbaum's lawyer maintained that Medicare did not lose any money because of the doctor's conduct.

Michigan ophthalmologist Matthew Burman was suspended by the state's Medicaid program in 2009 after he was convicted of a misdemeanor count of criminal sexual conduct arising from a patient's accusation against him. He was paid $379,000 by Medicare in 2012. (Medicare has not released payment data for prior years.) Burman, who continues to practice in Michigan, said he could have re-enrolled in Medicaid but chose not to. "One has nothing to do with the other," he said. "I didn't violate any Medicare rules. Medicare has nothing to do with why I'm not a Medicaid provider."

Louisville Dr. Steven Stern and his practice paid $350,000 to settle allegations of overbilling Medicare in September 2011. He and his practice were accused of overbilling Medicare for infusing Infliximab, a drug used to treat rheumatoid arthritis. In 2012, Stern received more than $3 million in payments from Medicare, including $2 million for infusing Infliximab. He did not return a phone call seeking comment.

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